WIP Allow not rerunning a cached dependency

* requires RKrahl/pytest-dependency#77, must
  document that somewhere (but it's "just convenience")

tests/install/conftest.py

@@ -1,10 +1,49 @@
 from copy import deepcopy
+import itertools
 import logging
 import os
 import pytest
 import tempfile
 
+from lib.common import shortened_nodeid
 from lib.commands import local_cmd, scp, ssh
+from lib.pool import Pool
+
+try:
+    from data import CACHE_IMPORTED_VM
+except ImportError:
+    CACHE_IMPORTED_VM = False
+assert CACHE_IMPORTED_VM in [True, False]
+
+def pytest_dependency_override_skip(item: pytest.Item, dependency: str, scope: str) -> bool:
+    if not CACHE_IMPORTED_VM:
+        return False
+    # FIXME duplicates parsing of --hosts, should use separate def instead
+    hosts_args = item.config.getoption("hosts")
+    hosts_split = [hostlist.split(',') for hostlist in hosts_args]
+    hostname_list = list(itertools.chain(*hosts_split))
+    if not hostname_list:
+        pytest.fail("pytest_dependency_override_skip requires at least one --hosts parameter")
+    pool = Pool(hostname_list[0])
+    host = pool.master
+
+    sr_uuid = host.main_sr_uuid()
+    dep_nodeid = _expand_scope_relative_nodeid(dependency, scope, item.nodeid)
+    if host.cached_vm(shortened_nodeid(dep_nodeid) + ".xva", sr_uuid):
+        return True
+    return False
+
+def _expand_scope_relative_nodeid(scoped_nodeid, scope, ref_nodeid):
+    if scope == 'session' or scope == 'package':
+        base = ()
+    elif scope == 'module':
+        base = ref_nodeid.split("::", 1)[:1]
+    elif scope == 'class':
+        base = ref_nodeid.split("::", 2)[:2]
+    else:
+        raise RuntimeError(f"Internal error: invalid scope {scope!r}")
+    logging.debug("scope: %r base: %r relative: %r", scope, base, scoped_nodeid)
+    return "::".join(itertools.chain(base, (scoped_nodeid,)))
 
 @pytest.fixture(scope='function')
 def answerfile(request):